Methods of producing refractory metal filaments of flattened zig-zag form



Apnl 7, 1959 D. J. JONES ET AL 2,

METHODS OF PRODUCING REFRACTORY METAL FILAMENTS 1 OF FLATTENED ZIG-ZAG FORM Filed Dec. 5, 1955 Fig.1

-v NToRS Dqvll) n/ wv JONES United States Patent 9 METHODS OF PRODUCING REFRACTORY METAL FILANIENTS OF FLATTENED ZIG-ZAG FORM David John Jones, Harrow, and Brian Stephen Gossling, Richmond, England, assignors to The General Electric Company Limited, London, England Application December 5, 1955, Serial No. 576,510

Claims priority, application Great Britain December 3, 1954 15 Claims. (Cl. 148-4) This invention relates to a method of producing filaments of refractory metal in the form of a flattened zig-zag.

In particular, the invention relates to the preparation of such filaments of relatively small dimensions that is to say dimensions such that if a zig-zag were made in known manner on a jig, the jig would be inconveniently small.

It is an object of this invention to produce a simple and effective method of producing such filaments.

According to this invention a method of making a filament of refractory metal in the form of a substantially flattened zig-zag comprises the steps of associating a filamentary spiral of said refractory metal with at least one ductile metal in a relatively compact structure pressing said structure into a substantially flattened shape, thus causing said ductile metal or metals to flow in contact with said spiral and thereafter chemically removing the ductile metallic material.

According to one aspect of this invention, a method of making a filament of refractory material in the form of a substantially flattened zig-zag comprises the steps of placing a filamentary spiral of refractory metal upon a relatively ductile metallic mandrel so as to form a relatively compact structure pressing said structure so as to flatten it to a desired extent, chemically removing the ductile metal and thereafter heat treating the flattened filament so as to set it.

According to alternative features of the present invention said pressing may take place at a temperature between 200 C. and 400 C. so that said refractory metal becomes relatively ductile. Either or both the spiral or ductile metal or metals may be heated before or during the pressing process so as to remove residual stresses.

One arrangement in accordance with the present invention will now be described by way of example with reference to a method of producing a filament of refractory metal in the form of a flattened zig-zag suitable for use as an electron source in an electron discharge device.

In this arrangement silica tungsten wire of diameter 0.125 mm. is wound on a tungsten wire mandrel of diameter 0.63 mm. to form a spiral having a pitch of 0.605 mm., the overall length of the spiral thus formed being 8 mm. The spiral is then removed from the tungsten mandrel and placed on an annealed cooper wire mandrel of diameter 0.604 mm. The spiral and the copper mandrel are then pressed between two plain hardened steel plates at a pressure of the order of five tons per sq. inch so as to cause the copper to flow in contact with the spiral which is thus flattened to the required extent. The flattened spiral and mandrel compact is then dipped in nitric acid so as to remove the copper and leave a flattened zig-zag filament of silica tungsten having an overall length of 9.5 mm. and a width of 1.4 mm. The flattened filament is then furnaced in a hydrogen atmosphere at a temperature of about 1400 C. for ten minutes. This serves to set the filament in its flattened zig-zag shape.

In an alternative arrangement the spiral having been placed on the mandrel is plated with copper to a depth of 0.5 mm. This is to ensure the rigid disposition of the spiral on the mandrel. Alternatively the spiral itself may be plated with copper to a suitable depth and then flattened without the necessity of placing the spiral on a mandrel. In another arrangement the filament is plated with copper to a suitable depth before being wound into a spiral. In further arrangements the spiral and the mandrel are annealed either separately or together either before or during the pressing, thus all residual stresses are removed from the materials. In still further arrangements the pressing takes place at a temperature such that the silica tungsten filament becomes relatively ductile, a suitable temperature being one of the order of 300 C.

A zig-zag silica tungsten filament prepared in accordance with the invention is particularly useful as an elec tron source in an electric discharge device such as for example, an X-ray tube or cathode ray tube. Such an electron source is capable of providing a very uniform electron distribution which is hence relatively simple to control.

One particular arrangement of an X-ray tube wherein an electron source is constituted by a zig-zag silica tungsten filament prepared in accordance with the invention will now be described with reference to the accompanying drawings, in which:

Figure l is a view of the filament; and

Figure 2 is a view, partly cut away to show internal details, of the X-ray tube.

Referring to Figure 2, the X-ray tube comprises a sealed evacuated glass envelope 1 in which is mounted an electrode structure. The electrode structure includes a cathode constituted by a silica tungsten filament 2 of flattened zig-zag form produced in accordance with the invention; the filament 2 (which is shown in detail in Figure 1) is disposed within a groove formed in a machined nickel cathode head 3, the filament 2 being disposed parallel to and slightly recessed from the face of the head 3 opposite a copper anode 4. A tungsten face 5 is formed upon the operating surface of the anode 4 and serves as a target. A window 6 is formed in the envelope 1 between the cathode and the target, the window 6 being constituted by a reduced thickness of the glass envelope.

In such an X-ray tube the useof such an electron source ensures the provision of one maximum in intensity at the focal spot in the transverse direction as opposed to two maxima from a conventional spiral filament and furthermore renders possible the production of a very fine focal spot.

It will be appreciated that whilst in the above arrangements silica tungsten and copper have been used as the refractory and relatively ductile metals respectively, other metallic materials possessing the same properties may also be used.

We claim:

1. A method of making a filament of refractory metal in the form of a substantially flattened zig-zag comprising the steps of placing a filamentary spiral of said refractory metal in intimate contact with at least one ductile metal so as to form a relatively compact structure in which said spiral is supported by said ductile metal, pressing said structure into a substantially flattened shape in which the spiral of refractory metal is flattened into zig-zag shape, thus causing said ductile metal or metals to flow in contact with said spiral and thereafter chemically removing the ductile metallic material.

2. A method of making a filament of refractory metal in the form of a substantially flattened zig-zag comprising the steps. of disposing a filamentary spiral of refractory metal around andin intimate contact with a relatively ductile metallic mandrel so as to form a relatively compact structure in which said spiral is supported by said ductile metal, pressing said structure so as to flatten it to an IBXtCl'lll such that the spiral of refractory metal is flattened into zig-zag shape, chemically removing the ductile metal and thereafter heat treating the flattened filament so as to set it.

3. A method of making a filament accordingto claim 1 in-which said pressing takes place at a temperature between 200 C. ,and 400 C. so that said refractory metal becomesrelatively ductile.

4. A method of making a filament according to claim 1 in which the spiral is heat treated before the pressing process so as to remove residual stresses.

5. A method of making a filament according to claim 1 in which said filament is plated with ductile metal before pressing.

6. A method of making a filament according to claim 1 in which said filament is formed of tungsten wire.

7. A method of making a filament according to claim 1 in which said ductile metal is copper.

8. A method of making a filament according to claim 1 in which the spiral is heat treated during the pressing process so as to remove residual stresses.

9. A method of making a filament according to claim 1 in which the ductile metal is heat treated before the pressing process so as to remove residual stresses.

10. A method of making a filament according to claim 1 in which the spiral and ductile metal are heat treated before the pressing process so as to remove residual stresses.

11. A method ofmaking a filament according to claim 1 in which the spiral and the ductile metal are heat treated during the pressing process so as to remove residual stresses.

12. A method of making a filament of refractory metal in the form of substantially flattened zig-zag comprising the steps of placing an open-wound filamentary spiral of said refractory metal in intimate contact with at least one ductile metal so as to form a relatively compact structure, in which said spiral is supported by said ductile metal, pressing said structure into a substantiallyfiattened shape in which the spiral of refractory metal is flattened into zig-zag shape, thus causing said ductile metal or metals to flow in contact with said spiral, and thereafter chemically removing the ductile metallic material.

13. A method of making a filament or refractory metal in the form of a substantially flattened zig-zag comprising the steps of placing a filamentary spiral of said refractory metal in intimate contact with at least one ductile metal so as=to form a relatively compact structure, in which said spiral is supported by said ductile metal, pressing said structure into a substantially flattenedshap'e without restraining longitudinal flow thereof under .pressureso that the ductile metal and spiral will spread in the direction of the length of the spiral, thereby flattening the spiral into a zig-zag. shape, thus causing said ductile metal or metals to flow in contact with said spiral, and thereafter chemically removing the ductile metallic material.

14. A method of making .a filament of refractory metal in the form of a substantially flattened zig-zag comprising the steps or placing a filamentary spiral of said refractory metal ,in intimate contact withat least one ductile metal so as to form a relatively compact structure, in which said spiral is supported by said ductile metal, pressing said structure into a substantially flattened shape without restraining transverse flow thereof under pressure so that the ductile metal and spiral will spread in a direction transverse to the length of the spiral, thereby flattening the spiral into a zig-zag shape, thus causing said ductile metal or metals to fiow in con tact with said spiral, and'thereafter chemically removing the ductile metallic material.

15. A method of making a filament of refractory metal in'the form of a substantially flattened zig-zag comprising the steps of placing a filamentary spiral of said refractory metal in intimate contact with at least one ductile metal so as to form a relatively compact structure, in which said spiral is supported by said ductile metal, pressing said structure into a substantially flattened shape without restraining longitudinal or transverse .flow thereof under pressure so that the ductile metal and spiral will spread parallel and transverse to the length of the spiral, thus causing said ductile metal or metas to flow in contact with said spiral, and thereafter chemically removing the ductile metallic material.

References Cited in the file of this patent UNITED STATES PATENTS 1,738,960 ,Mutscheller Dec. 10, 1929 2,047,555 Gardner July 14, 1936 2,069,081 Setoguchi Jan. 26, 1937 2,165,310 Spaeth July 11, 1939 2,482,826 Bender et al. Sept. 27, '1949 

1. A METHOD OF MAKING A FILAMENT OF REFRACTORY METAL IN THE FORM OF A SUBSTANTIALLY FLATTENED ZIG-ZAG COMPRISING THE STEPS OF PLACING A FILAMENTARY SPIRAL OF SAID REFRACTORY METAL IN INTIMATE CONTACT WITH AT LEAST ONE DUCTILE METAL SO AS TO FORM A RELATIVELY COMPACT STRUCTURE IN WHICH SAID SPIRAL IS SUPPORTED BY SAID DUCTILE METAL, PRESSING SAID STRUCTURE INTO A SUBSTANTIALLY FLATTENED SHAPE IN WHICH THE SPIRAL OF REFRACTORY METAL IS FLATTENED INTO ZIG-ZAG SHAPE, THUS CAUSING SAID DUCTILE METAL OR METALS TO FLOW IN CONTACT WITH SAID SPIRAL AND THEREAFTER CHEMICALLY REMOVING THE DUCTILE METALLIC MATERIAL. 